1. Field of the Invention
The present invention relates to a swash plate type compressor for compressing a refrigerant gas, by rotating a swash plate. More particularly, the present invention relates to an improvement to swash plate compressors by applying a fluorocarbon coating on the swash plate facial surfaces and ends to reduce the frictional wear on the components. The coated swash plate may be made from lower cost alloy materials while maintaining durability and efficiency.
2. Description of the Related Art
Swash plate compressors have been used in automotive air conditioning systems for many years. In a swash plate type compressor, a swash plate rotates about a shaft. A number of pistons are arranged radially about the perimeter of the swash plate and slide within cylinder bores positioned parallel to the shaft. The facial and end surfaces of the swash plate contact pivoting shoes within the pistons. The rotation of the swash plate reciprocates the pistons. The reciprocating swash plate has a relatively high surface area that contacts the piston shoes. In addition to the large contact area, the type of contact also causes a large amount of friction. The rotating swash plate undergoes a shear-type contact with the piston shoes. The shearing force of the contact wears away many types of friction reducing coatings. The interfacial surfaces between the swash plate and pistons are subject to very high load conditions and are susceptible to premature wear before the remainder of the compressor. Protecting these surfaces from wear increases the life of the compressor and also increases the compressor efficiency.
It is known to coat the surface of an aluminum swash plate to reduce wear. Coatings as described in U.S. Pat. No. 5,056,417, issued Oct. 15, 1991, to Kato et al., include 50% by weight of tin and lesser portions of copper, nickel, zinc, lead and indium to form a metal matrix coating. Coatings of this type are electrolytically applied and usually require that the base material have a highly polished surface to provide maximum durability. These electroplated coatings also require that the swash plate be made from aluminum or aluminum alloy materials that contain hard second phase particles. Hard second phase particles mean second phase particles having an average particle diameter of 200 through 100 micrometers (.mu.m) and a hardness greater than 300 on the Vicars hardness scale or, more preferably, having a hardness greater than 600 on the Vicars hardness scale, such as primary silicon. Especially preferred is an aluminum silicon alloy containing about 13 percent to 30 percent by weight of silicon. The high silicon aluminum and tin metal matrix coating gives the coated swash plate increased durability, but at the expense of frictional resistance.
To enhance the frictional properties of the electroplated swash plate, the 5,056,417 patent teaches the use of a solid lubricant such as fluororesin as part of the metal matrix coating. The fluororesin was added to the aqueous solution used in the chemical plating process. While the fluororesin coating provided a swash plate with a lower coefficient of friction, the surface coating layer exhibited a lower hardness than the tin matrix coating alone and was more susceptive to rapid abrasion.
Electroplated metal matrix coatings on aluminum components are acceptable under light loads, they have several disadvantages when used under high friction loads including the need for expensive, high silicon aluminum base materials; high surface finishing for the base material and a complex electroplating process. Adding the fluororesin to the metal matrix improved the coefficient of friction, but at the expense of surface hardness and durability.
It is desirable to provide a coating on a swash plate that is both friction reducing and highly durable. It is also desirable to provide a coating that permits the use of lower cost, low silicon aluminum base material for the swash plate. It is further desirable to provide a swash plate coating that does not require the need to electroplate the surface of the swash plate. These and other advantages of the present inventions will be more fully described below and in the accompanying drawings.